April Fools' Day: The Neuroscience of Humor

What makes an April Fools' prank hilarious? A cognitive scientist's (actually funny) new book shows how the brain breaks down the elements of a joke and why we laugh. Sharon Begley reports.

(Photo by Jim Arbogast / Getty Images),Jim Arbogast

If you don’t care about damage to your reputation, career, or marriage, there is no shortage of April Fools' Day pranks you can pull, such as gluing someone’s handset to his landline phone and then calling him from nearby (anywhere with sight lines to the entire phone getting lifted to his ear) or—a classic—balancing a paper cup of water atop a partially open door. While reasonable people can debate whether the results are hilarious or sophomoric, chances are a disinterested observer would at least crack a smile. Cognitive scientist Matthew Hurley of Indiana University wanted to know why.

The result, as laid out in a new book, Inside Jokes: Using Humor to Reverse-Engineer the Mind, is the most persuasive theory of humor in the centuries that scientists have been trying to explain why we crack up. Extra bonus: unlike most such research, which is about as funny as a root canal, Hurley’s analysis is—and I don’t think I’m going out on too much of a limb here—the funniest thing the MIT Press (home of Knowledge Management in Theory and Practice and Edge-Based Clausal Syntax) has ever published (in a good way).

Written with philosopher Daniel Dennett of Tufts University and psychologist Reginald Adams of Pennsylvania State University, Inside Jokes argues that mirth (the feeling we experience when we encounter humor) arises when the brain realizes that an assumption it has committed to is flat-out wrong.

That sounds simplistic, so here’s the long version: The brain constantly generates presumptions about what will happen next. It calculates where a pedestrian will go, what a speaker will say, how a banana you’re peeling will look under the skin. In short, the brain “produc[es] real-time anticipation on all important topics,” argue the authors, as it generates myriads of possible futures, and also fills in details about ambiguous situations in the present—both of which are crucial to functioning in a world of imperfect and incomplete information.

For instance: Two goldfish are in their tank, and one says to the other, “You man the guns, I’ll drive.”

If you smiled, it’s because your brain saw “tank” and assumed “fish tank.” Humor is what we perceive when we make a mistaken assumption and discover it. By making mirth pleasurable, Hurley and his co-authors argue, evolution has sculpted a mechanism that bribes us to continue generating such assumptions and filling in details in ambiguous situations, without which we could not function in the world.

A good example of how the brain fills in possible futures is this limerick:

There was a young lady named Tuck, Who had the most terrible luck She went out in a punt, And fell over the front, And was bit on the leg by a duck.

If you found it even a little funny, it was because your brain made an assumption about the last line and filled in other possibilities. It will do so as you follow this story, too:

O’Connell was late for a meeting and in a panic as he looked for a parking spot. Turning his face to the sky, he said, “Lord help me. If you give me a parking spot, I will go to church every Sunday for the rest of me life and quit drinking me Irish Whiskey!” Just then, out of nowhere, a parking spot appeared in front of him. O’Connell looked up again and said, “Never mind, I found one.”

If you laughed, or even smiled—as Hurley did, since this joke is one of his favorites lately—it is because you assumed one thing about how O’Connell would react and were surprised to read otherwise. Kudos: the more you generate possible futures and make assumptions to fill in the blanks in the world, the better your cognitive function. “Intelligence is significantly lacking if humor is absent; we would make significantly more mistakes without it,” Hurley argued in an interview. People are right to use a sense of humor as a sign of intelligence.

The science of humor is hardly virgin terrain. There are almost as many theories of what makes something funny as there are light-bulb jokes, with scholars from Schopenhauer to Kant trying their hand. ( One recent theory offers an equation to explain humor). But all of them fall short. The theory that mirth is triggered by things that make us feel superior? No: you don’t feel superior to goldfish. The theory that something is funny if it releases aggressive or sexual tension? No: photons have mass? I didn’t even know they were Catholic. If your humor detector went off, it wasn’t because the joke relieved tension. The theory that surprise alone is enough for humor? No: An atheist exploring the deepest Amazon is suddenly surrounded by ferocious cannibals, and says to himself, oh God, I’m screwed. Suddenly a beam of light shoots down from the sky and a voice booms out, “No, you are not screwed. Just pick up that rock by your feet and use it to bash in the chief’s head.” The explorer did as instructed and bashed the living heck out of the chief. Standing above the lifeless body as the astonished warriors looked on, he heard the voice again: “Now you’re screwed.” But while that’s a surprise ending, so are many stories that we don’t find funny at all. Replace the ending above with “so the warriors all walked off”—not likely to make you crack a smile.

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The most popular theory holds that humor arises when an incongruity is present. To wit:

The desperate patient knocked and knocked at the physician’s door, and when it was opened rasped out, “Is the doctor home?” “No,” whispered the doc’s pretty young wife; “Come right in.”

The incongruity between what (we think) the patient wants and what the wife thinks he means is funny. However, motion sickness, too, arises from an incongruity (between our balance system telling us we’re moving a lot and the visual system saying not so much), but we respond to that by vomiting, not laughing.

“Our explanation of humor uses insights from earlier theories, but pulls them all together because, in some way, they are all correct about some part of it,” says Hurley. “There is surprise in humor, there is superiority in humor, there is incongruity in humor, there is playfulness in humor.” (What’s green, alive, found all over suburbia, and has 17 legs? Grass; I lied about the legs.) Hence the humor in April Fools' pranks, too.

The missing ingredient in earlier theories is the particular kind of surprise and incongruity that is necessary to find something funny. The surprise, says Hurley, must arise from realizing that we made a mistake as a result of implicit assumptions, not explicit thought, or from misunderstanding information that is introduced covertly rather than explicitly. And crucially, the discovery of that mistake must not cause sadness, fear, or other negative emotion. If we go to a lecture and (explicitly) expect to hear about bird watching, only to be subjected to a speech on 16th-century poetry, we’re unlikely to find it humorous. Similarly, if the joke had stated explicitly that the goldfish are in a military tank, the punch line would fall flat.

Feeling mirth is the brain’s way of telling us that we committed too soon to one interpretation of reality or to one assumption about the future. For instance, how do you get a philosopher off your porch? Pay for the pizza. Here the mistake is imagining a latter-day Plato hanging out on your porch, cogitating on epistemology. Or, a man walks into a bar, with a frog on his nose. The bartender asks, “how did you get that?” A tiny voice replies, “Well, it started with a big wart on my behind.” The assumption that the bartender was addressing the man is shattered. Or, I want to die peacefully in my sleep like my grandfather . . . not screaming in terror like his passengers. Mistake: thinking grandpa died in his bed, not at the wheel of a bus. By making the discovery of this kind of mistake pleasurable, the brain bribes us to keep making assumptions and extrapolating futures, which (mistakes and all) is indispensable for navigating the world.

Penn Jillette, the speaking half of Penn & Teller, has blurbed it, saying, “I’m so glad smart people outside of comedy are taking comedy seriously.” Scientists will weigh in on the validity of the new theory of humor, but give Hurley and his colleagues credit for this: They have written a book dissecting humor without killing the patient.

Plus: Check out Book Beast, for more news on hot titles and authors and excerpts from the latest books.

Sharon Begley is the science columnist and science editor of Newsweek. She is the co-author of the 2002 book, The Mind and the Brain, and the author of the 2007 book Train Your Mind, Change Your Brain.